Non-staining triarylmethane color base and method of printing therewith



March 1, 1960 c. DAVIS 2,927,040

NON-STAINING TRIARYLMETHANE COLOR BASE AND METHOD OF PRINTING THEREWITHFiled Aug. 13, 1957 lW////////////////////// //////1 B A BASE WEBINVENTOR CHESTER DAVIS ATTORNEY N ON-STAINING TRIARYLMETHANE COLOR BASEAND METHOD OF PRINTING THEREWIT H The purposeof this invention is todescribe a simple recording system which is nonstaining to skin andclothing. This involves the preparation and use of triphenylmethane dyederivatives which are incapable of chemical adsorption by the normalconstituents of skin tissue and textile fibers.

Staining of tissue may be chemical or physical; that is, a chemicalcompound with tissue may be formed or a colored substance may bephysically entrapped by tissue without reacting with the tissue itself.In the case of chemical staining, repeated washing with soap and waterusually has little or no effect; but this washing treatment usuallyremoves physically absorbed colors with ease. Chemical staining of skinand clothing is by far the most objectionable feature in recordingsystems involving the use of triphenylmethane dyes.

For many years the high color intensity of the triphenylmethane dyes(Malachite Green, Crystal Violet, etc.) has prompted their use inbusiness recording systems, especially where multiple copies aredesired. A spirit duplicating master sheet containing Crystal VioletOleate, for example, may give two to five times more satisfactory copiesthan an azo-dye-forming master sheet; and the requirement that ballpoint pen inks have high color intensity necessitates the use ofVictoria Blue and similar triphenylmethane dyes. Unfortunately, copyfluids and copy papers containing these materials cause permanentchemical staining of skin tissue and clothing fabrics; and workers inthe recording field have long sought means of overcoming this basicdefect.

The reduction of triphenylmethane dyes to their colorless leucocompounds and the conversion of their dye salts to the colorlesscarbinol bases by means of strong alkalis has been proposed in one formor another by previous workers in the recording field, but thesesubstances are readily converted back to the intensely colored dye saltsby air, sunlight, skin and clothing with consequent strong chemicaladsorption. Davis and Thacker (US. 2,646,367) have utilized certaincolorless triphenylmethane lactones which are nonstaining to skin, butthese materials are extraordinarily unstable to light and moisture inthe colored form. What is needed for commercial recording systems is aseries of triphenylrnethane dye compounds which are substantiallynonstaining to skin and clothing, cheap, reasonably lightstable in thecolored form, and giving on a suitable surface colored characters whichare resistant to decoloration by high humidity and adverse atmosphericconditions.

The author of the present invention has chosen to examine the problemfrom a new theoretical viewpoint as to theexact mechanism of staining bythese dyes.

The high bactericidal activity of the acridine dyes has been shown byAlbert and Goldacre (Nature, 161, 95

States atent Patented Mar. 1, 1960 'ice (1948)) to be closely related tothe disassociation constant of their bases; and it is significant thatGentian Violet Base has a dissociation constant of (pKa9) which is veryclose to the optimum required for maximum adsorption by the livingbacterial cell. Michlers Hydrol is a much weaker base (pKa6) thanGentian Violet Base and is also much weaker in bactericidal and stainingproperties. An analysis by the author of the present invention of theavailable data indicated that the essential factor for a non-stainingtriphenylmethane color base would appear to be a dissociation constantbelow with skin tissue yet is still sufficiently acidic to giveintensely colored salts with suitable acids, including the paper coatingacid clays and acid silicas which have long been used for preparingcoated papers for use in the copy paper field.

The resultant nitrated color bases are yellow to orangered in color,stable, and readily yield light-stable, intense prints on suitablereceiving sheets. Dinitro Crystal Violet Carbinol Base (I) and DinitroMalachite Green Carbinol Base (II), for example, upon solution insuitable organic solvents give strong yellow solutions which can befreely handled without leaving intense violet or green stains upon theskin. The resultant recording fluids, however, will give intensecharacters upon transfer to a suitable recording surface.

Previous workers in the recording field have concentrated theirinvestigations on attempts to obtain completely colorless derivatives ofthe triphenylmethane dyes; these workers failed to realize that the mostdesirable feature of recording colors is a complete lack of stain andnot a complete lack of color, which is a secondary consideration. Acolored recording system of high intensity and lacking in chemicalstaining properties is far more desirable that a colorless system of lowtinctorial power or low stability or which stains the skin. It is,therefore, not the purpose of the present invention to claim anabsolutely colorless recording system. The point to be emphasized is thelack of permanent chemical stain possessed by compounds of the presentinvention.

ture (IV) is stable at a higher proton concentration be cause here thequanticule of one benzene ring is less free to shield the central carbonatoms charged core and the screening contribution of the hyroxylquanticule is more strongly needed. Upon dinitration, the resultantstructure is such that now two quanticules are less free to shield thecentral core; and the hydroxyl quanticule is now strongly required forscreening the central car bon atoms charged core. In brief, thedissociation constant is decreased and Dinitro Crystal Violet CarbinolBase is a weak base. The Trinitro Crystal Violet Car binol Base (V) hassuch a strong screening requirementfor the hydroxyl quanticule thatdissociation can occur only at high proton concentrations; and V is avery weak base.

IIlMez $Mez \L I, 25 E I O-NO:

I NMea MezN-Q-XEECWQOH I ONO: NMG:

In place of a proton, one may use a Lewis acid for removing a quanticule(electron pair) from the screening electrons around the central carboncore. The most suitable Lewis acids for commercial purposes are the acidsilicates, such as clays, fullers earth, activated slica, and similarmaterials which have an acid strength equivalent to a pH below 5,preferably from 1 to 4. These solid acids are sufiiciently strong thatthey form stable colored salts with the nonstaining color bases of thepresent invention.

For certain applications, the use of performed dye salts of thenonstaining color bases would be preferable to the use of the free basesthemselves; this removes the need for a specially coated receiving sheetand permits the use of standard paper as a receiving sheet. The use ofoleic acid and organic acids such as trichloracetic and tannic acid isideal for these applications. Any colored salts which accidentallycontact fibers can be easily removed by treatment with a mild alkali(soap, ammonium hyroxide solutions, triethanolamine solutions, etc.) andsubsequent washing with water or a wool-cleaning solvent such as carbontetrachloride.

All that is essential for the purpose of the present invention is areduction of the dye base dissociation constant to a value sufficientlybelow pK 7 that reaction with constituents of skin tissue and textilefibers is negligible. The best results are obtained with materials ofdissociation constant between pK 2 and 5. This is accomplished by thesuitable introduction of nitro groups into the triphenylmethane aromaticrings. While the products from Crystal Violet and Malachite Green are ofspecial interest because of the fundamental simplicity of thesestructures and their low cost, the process is generally applicable tothe entire field of the triphenylmethane dyes and their closed ringanalogues.

Description Because the triphenylmethane dyes and most of theirmononitro derivatives stain the skin, it is essential that the startingmaterials and intermediate nitration products be absent from thenonstaining derivatives obtained by controlled nitration. This is bestachieved by careful control of the amounts of nitric acid used and thetemperature at which the reaction is carried out.

gms. (0.257 mol) of Crystal Violet Carbinol 'Base or a correspondingamount of the colored dye salt is dissolved in 1500 gms. of concentratedsulfuric acid; and the resultant solution is cooled to 03 C. To the colddye solution is added with stirring a cold solution of 51.7 gms. (0.517mol) of 63% concentration nitric acid in 400 gms. concentrated sulfuricacid, maintaining the reaction temperature below 8 C., usually around3-5 C. The solution is allowed to stand for one hour at 3-5 C. and thenslowly warmed to 25 C. After one hour at 25 C., the sulfuric acid ispoured onto a large amount of crushed ice and water. The resultingsulfuric acid solution is neutralized with a suitable base, usuallyammonium hydroxide solution or caustic soda solution to precipitate out2,2-dinitro-4,4',4"-tris (dimethylamino)-triphenylcarbinol (DinitroCrystal Violet Carbinol Base). This is thoroughly washed with water anddried to give a yellow-green powder which is pure enough for mostpurposes; however, the slightly impure product can be further purifiedby recrystallization from acetone-Water or by resolution in dilutemineral acids followed by reprecipitation by base at a pH of 6-7.

100 gms. (0.257 mol) of Crystal Violet Carbinol Base or a correspondingamount of the dye salt is dissolved in 1500 gms. of concentratedsulfuric acid; and the resultant solution is cooled to 0-3 C. To thecold dye solution is added with stirring a cold solution of 76.9 gms.(0.785 mol) of 63% concentration nitric acid in 400 gms. of concentratedsulfuric acid, maintaining the reaction temperature below 10 C., usuallybetween 35 C. After one hour at 5 C., the temperature of the reactionmixture is slowly raised to 25 C. and maintained at 25 C. for one hour.The reaction mixture is then poured onto a large amount of crushed iceand water;

and the resulting acid solution is then neutralized with base toprecipitate out 2,2',2"-trinitro-4,4,4"-tris(dimethylamino)-triphenylcarbinol (Trinitro Crystal Violet CarbinolBase). This is filtered off, thoroughly washed with water, and dried toyield a light green powder. The product may be further purified byresolution in mineral acids and reprecipitation with base at a pH of6.

100 gms. (0.289 mol) of Malachite Green Carbinol Base or a correspondingmolar equivalent of the dye salt is dissolved in 1500 gms. ofconcentrated sulfuric acid; and the resultant solution is cooled to 0 C.To the'cold dye solution is added with stirring a cold solution of 5:8.1gms. (0.581 mol) of 63% concentration nitricacidin400 gms. concentratedsulfuric acid, maintaining the reaction mixture below 8 C., usuallybetween 2-5 C. After one hour at 5 C., the temperature of the reactionmixture is slowly raised to 25 C. and maintained at 25 C. for one hour.The reaction mixture is then poured onto a large amount of crushed iceand water, and the resulting acid solution is neutralized with base toprecipitate out 2,2- dinitro-4,4'-bis (dimethylamino) triphenylcarbinol.This is filtered 01f and washed thoroughly with water to yield ayellow-green powder. The product may be purified by resolution in dilutemineral acids and reprecipitation with base at a pH of 6.

The mononitration product, 2-nitro-4,4-bis (dirnethylamino)tn'phenylcarbinol, can be obtained by the use of one equivalent ofnitric acid; this has very slight staining properties and is suitablefor certain uses. The mononitro compound, 2"-nitro-4,4-bis(dimethylamino) triphenylcarbinol, which is obtainable by thecondensation of ortho-nitrobenzaldehyde with dirnethylaniline, possessesstrong staining properties.

100 gms. (0.267 mol) of Methyl Violet Carbinol Base or a correspondingamount of the dye salt is dissolved in 1500 grns. of concentratedsulfuric acid; and the resultant solution is cooled to 3-5 C. i To thecold dye solution is added with stirring a cold solution of 53.3 gms.(0.534 mol) of 63% concentration nitric acid in 400 gins. ofconcentrated sulfuric acid, maintaining the reaction temperature below8' C., usually between 35 C. The reaction mixture is allowed to standfor one hour at 3-5 C. and then slowly warmed to 25 C. After one hour at25 C., the sulfuric acid reaction mixture is poured onto a large amountof crushed ice and water. The resulting acid solution is neutralizedwith ammonium hydroxide solution to precipitate out2,2-dinitro-N,N,N"-pentamethyl-4,4,4"-triaminotriphenylcarbin0l (DinitroMethyl Violet Carbinol Base). This is thoroughly washed with water anddried to give a yellow-green powder which is pure enough for mostpurposes; the slightly impure product can be further purified byresolution in dilute mineral acids followed by reprecipitation with baseat a pH of 6-7.

A general rule is that the triaminotriphenyl methane dyes require atleast two nitro groups for adequate reduction of basicity anddiaminotriphenylmethane dyes require at least one and preferably twonitro groups. The nitro group must be attached to the aromatic nucleuscontaining the basic substituent in order to reduce the quanticuledonating eifect of the amino aromatic system. The principle can beapplied to all types of basic triphenylmethane dyes and their closedring analogues; and variations are readily obvious to one skilled in theart, once the fundamental principle is known.

An example of a recording fluid containing a nonstaining color base is a3% solution of 2,2'-dinitro 4,44"-tris (dimethylamino)-triphenylcarbinol(Dinitro Crystal Violet Carbinol Base) in toluene. This gives an intensedark violet (almost blue-black) coloration on a receiving sheet coveredwith an activated silica coating.

Another example of this invention is a 3% solution of2,2',2"-trinitro-4,4'4"'tris(dimethylamino) triphenylcan binol (TrinitroCrystal Violet Carbinol Base) in alcohol. This gives an intense darkviolet (almost blue-black) coloration on a receiving sheet coated with acolloidal silicate acid (kaolin, etc.).

Still another example of this invention is a 2.5% solution of Z-NitroMalachite Green Carbinol Base in chlorinated diphenyl of 42% chlorinecontent. This gives an intense green coloration on a receiving sheetcoated with calcium silicate.

Still another example of this invention is a 4% solution in alcohol ofthe colored dye salt from Dinitro Crystal Violet Carbinol Base andbenzenesulfonic acid. This gives an intense violet coloration on anordinary paper receiving sheet.

It should be clearly understood that the invention is not limited to theexamples set forth but is generally applicable to the entire family ofbasic triphenylmethane dyes and their closed ring analogues (notably theXanthines) which may undergo suitable nitration to form weak basesincapable of reacting chemically with skin tissue and textile them yetare capable of reacting with stronger acids to form stable coloredsalts.

The drawing is a cross-sectional view illustrative of a other words, therecording media ofthis: invention may be used in a great variety ofrecording, printing, and manifolding systems. The utilization of myinvention by means of a transfer sheet is particularly disclosed in myco-pending application Serial No. 677,838, filed August 13, 1957, forNonstaining Transfer Sheet.

Having described my invention, I claim:

1. The method of printing which comprises applying to a surfacecharacterized by high acid strength a substantially nonstaining liquidwhich comprises, a nonstaining triarylmethane color base containing atleast two dialkylamino-substituted aryl groups having as a substituent anitro group and characterized by a logarithmic dissociation constantbetween 2 and 5, said nonstaining triarylmethane color base beingstructurally adapted to react with the acid surface to form an intenselycolored salt.

2. The method of printing which comprises applying to a surfacecharacterized by high acid strength a substantially nonstaining liquidwhich comprises a nonstaining triarylmethane color base containing atleast dialkylamino-substituted aryl groups having as a substituent orthoto the central carbon atom a nitro group and characterized by alogarithmic dissociation constant between 2 and 5, said nonstainingtriarylmethane color base being structurally adapted to react with theacid surface to form an intensely colored salt.

' 3. The method of claim 1 wherein the nonstaining triarylmethane colorbase is a member of the group consisting ofN,N',N"-alkylated-2,2'-dinitro-4,44"-triaminotriphenylcarbinols andtheir carbinol others.

4. The method of claim 1 wherein the nonstaining triarylmethane colorbase is a member of the group consisting ofN,N',N"-alkylated-2,2',2"-trinitro-4,4,4"-triaminotriphenylcarbinols andtheir carbinol ethers.

5. The method of claim 1 wherein the nonstaining triarylmethane colorbase is a member of the group consisting ofN,N-alkylated-2,2'-dinitro-4,4'-diaminotriphenylcarbinols and theircarbinol ethers.

6. The method of printing which comprises applying to a surface havingthereon a silicate coating of high acid strength a substantiallynonstaining liquid which comprises a nonstaining triarylmethane colorbase containing at least two dialkylamino-substituted aryl groups havingas a substituent a nitro group and characterized by a logarithmicdissociation constant between 2 and 5, whereby contact of thenonstaining triarylmethane color base and the acid silicate causes theformation of an intensely colored triarylmethane colored salt to form acolored print.

7. The method of printing which comprises applying to a surface havingthereon a silicate coating of high acid strength a substantiallynonstaining liquid which comprises a nonstaining triarylmethane colorbase containing at least two dialkylamino-substituted aryl groups havingas a substituent ortho to the central carbon atom a nitro group andcharacterized by a logarithmic dissociation constant between 2 and 5,whereby contact of the nonstaining triarylmethane color base and theacid silicate causes the formation of an intensely coloredtriarylmethane colored salt to form a colored print.

'8. The method of claim 7 wherein the nonstaining triarylmethanecolor'base is a member of the group consisting ofN,N',N"-alkylated-2,2'-dinitro-4,4,4"-triaminotriphenylcarbinols andtheir carbinol ethers.

9. The method of claim 7 wherein the nonstaining triarylmethane colorbase is a member of the group consisting ofN,N,N"-alkylated-2,2',2"-trinitro-4,4',4-tIiaminotriphenylcarbinols andtheir carbinol ethers.

10. The method of claim 7 wherein the nonstaining triarylmethane colorbase is a member of the group of N,N-alkylated2,2-dinitro-4,4-diaminotriphenylcarbinols and their carbinol ethers.

11. The method of printing which comprises applying to a receptivesurface a substantially nonstaining liquid which comprises asubstantially nonstaining colored salt of a nonstaining triarylmethanecolor base containing at least two dialkylamino-substituted aryl groupshaving as a 'substituent a nitro group and characterized by alogarithmic dissociation constant between 2 and 5, said colored salthaving too low an ionization constant to undergo a permanent chemicalreaction with the constituents of human skin.

12. 'The method of printing which comprises applying to a receptivesurface a substantially nonstaining colored salt of a nons'tainingtriarylmethane color base containing at least twodialkylamino-substituted aryl groups having as a substituent ortho tothe central carbon atom a nitro group and characterized by a logarithmicdissociation constant between 2 and 5, said colored salt having too lowan ionization constant to undergo a permanent chemical reaction withhuman skin.

13. A printing medium comprising a substantially nonstainingtriarylmethane color base containing at least twodialkylaminosubstituted aryl groups having as a substituent a nitrogroup and characterized by a logarithmic dissociation constant between 2and 5, said compound dissolved in a solvent therefor, said compoundbeing structurally adapted to form an intensely colored salt uponcontact with a surface characterized high acid strength.

14. A printing medium comprising the colored salt of a nonstainingtriarylmethane color base containing at least'twodialkylamino-substituted aryl groups having as a substituent a nitrogroup and characterized by a logarithmic dissociation constant between 2and 5, said colored salt dissolved in a solvent therefor, said coloredsalt having too low an ionization constant to undergo a per manentchemical reaction with human skin.

15. A new composition of matter comprising a substantially nonstainingtriarylmethane color base containing at least twodialkylamino-substituted aryl groups having as a substituent a nitrogroup, the logarithmic dissociation constant of which is within therange 2 to 5, whereby said nonstaining triarylmethane color base becomeschemically unreactive towards human skin but reacts with strong acids toform an intensely colored salt.

16. A new composition of matter represented by the following formula:

wherein R is a lower alkyl group and R is chosen from the groupconsisting of hydrogen and lower alkyl.

17. A new composition of matter comprising the intensely colored saltsobtained by the reaction of the non-I staining color base of claim 16with a strong acid.

18. A new composition of matter represented by the following formula:

wherein R is a lower alkyl group and R is chosen from the groupconsisting of hydrogen and lower alkyl.

19' A new composition of matter comprising the intensely colored saltsobtained by the reaction of the nonstaining color base of claim 18 witha strong acid.

20. A new composition of matter represented by the following formula:

wherein R is a lower alkyl group and R is chosen from the groupconsisting of hydrogen and lower alkyl.

21. A new composition of matter comprising the intensely colored .saltsobtained by the reaction of the nonstaining color base of claim 20 witha strong acid.

References Cited in the file of this patent UNITED STATES PATENTS2,755,201 Webber July 17, 1956 2,755,202 Balon July 17, 1956 2,755,203Stallman July 17, 1956 i Z i r

1. THE METHOD OF PRINTING WHICH COMPRISES APPLYING TO A SURFACECHARACTERIZED BY HIGH ACID STRENGTH A SUBSTANTIALLY NONSTAINING LIQUIDWHICH COMPRISES A NONSTAINING TRIARYLMETHANE COLOR BASE CONTAINING ATLEAST TWO DIALKYLAMINO-SUBSTITUTED ARYL GROUPS HAVING AS A SUBSTITUENT ANITRO GROUP AND CHARACTERIZED BY A LOGARITHMIC DISSOCIATION CONSTANTBETWEEN 2 AND 5, SAID NONSTAINING TRIARYLMETHANE COLOUR BASE BEINGSTRUCTURALLY ADAPTED TO REACT WITH THE ACID SURFACE TO FORM AN INTENSELYCOLORED SALT.